排序方式： 共有30条查询结果，搜索用时 31 毫秒
1.
This paper presents a numerical model for predicting the dynamic response of rock mass subjected to large‐scale underground explosion. The model is calibrated against data obtained from large‐scale field tests. The Hugoniot equation of state for rock mass is adopted to calculate the pressure as a function of mass density. A piecewise linear Drucker–Prager strength criterion including the strain rate effect is employed to model the rock mass behaviour subjected to blast loading. A double scalar damage model accounting for both the compression and tension damage is introduced to simulate the damage zone around the charge chamber caused by blast loading. The model is incorporated into Autodyn3D through its user subroutines. The numerical model is then used to predict the dynamic response of rock mass, in terms of the peak particle velocity (PPV) and peak particle acceleration (PPA) attenuation laws, the damage zone, the particle velocity time histories and their frequency contents for large‐scale underground explosion tests. The computed results are found in good agreement with the field measured data; hence, the proposed model is proven to be adequate for simulating the dynamic response of rock mass subjected to large‐scale underground explosion. Extended numerical analyses indicate that, apart from the charge loading density, the stress wave intensity is also affected, but to a lesser extent, by the charge weight and the charge chamber geometry for large‐scale underground explosions. Copyright © 2004 John Wiley & Sons, Ltd. 相似文献
2.
HU Huiqin HUANG Fei ZHANG Shaoqing RUAN Chengqing GAO Shanhong LI Pengyuan 《中国海洋大学学报(英文版)》2019,(2):271-281
Fog has recently become a frequent high-impact weather phenomenon along the coastal regions of North China. Accurate fog forecasting remains challenging due to limited understanding of the predictability and mechanism of fog formation associated with synoptic-scale circulation. One frequent synoptic pattern of fog formation in this area is associated with cold front passage(cold-front synoptic pattern, CFSP). This paper explored the predictability of a typical CFSP fog event from the perspective of analyzing key characteristics of synoptic-scale circulation determining fog forecasting performance and the possible mechanism. The event was ensemble forecasted with the Weather Research and Forecasting model. Two groups of ensemble members with good and bad forecasting performance were selected and composited. Results showed that the predictability of this case was largely determined by the simulated strengths of the cold-front circulation(i.e., trough and ridge and the associated surface high). The bad-performing members tended to have a weaker ridge behind a stronger trough, and associated higher pressure over land and a weaker surface high over the sea, leading to an adverse impact on strength and direction of steering flows that inhibit warm moist advection and enhance cold dry advection transported to the focus region. Associated with this cold dry advection, adverse synoptic conditions of stratification and moisture for fog formation were produced, consequently causing failure of fog forecasting in the focus region. This study highlights the importance of accurate synoptic-scale information for improved CFSP fog forecasting, and enhances understanding of fog predictability from perspective of synoptic-scale circulation. 相似文献
3.
Natural Hazards - Natural hazards, such as high winds, heavy rains and ice melting, can easily trigger the rockfall which usually leads to great personal injuries and property loss; therefore, the... 相似文献
4.
建立了基于有限断层的芦山地震的混合震源模型,突出破裂面上滑动量分布中凹凸体的主导作用,同时借助k平方模型表达对震源复杂性认识尚不够深入所带来的随机性.混合震源模型中全局震源参数均值与局部震源参数均值的确定,主要依据统计的半经验标定公式,进一步借助截断正态分布将区域地震、地质构造、地震活动性提供的参数限值结合起来,生成最终的震源参数值.基于上述思路,本文共建立了30组芦山地震混合震源模型,进而以芦山地震8个近场观测台站为试算点,借助地震动反应谱残差评价的方法,从30组模型中选定了表达“平均”特征的混合震源模型. 相似文献
5.
Sedimentary Phosphorus Form Distribution and Cycling in the Littoral Subzones of a Eutrophic Lake 总被引：2，自引：0，他引：2
Algae which bloom in open water and accumulate in the littoral zones may affect the biogeochemical cycle of phosphorus in eutrophic lakes. To determine such effects, a part of the lakeshore with little allochthonous nutrient input in Taihu Lake, China was selected for this field study. Distinct differences in sedimentary P forms were found among the different littoral subzones. The surface sedimentary total phosphorus (TP) content was 655 mg/kg in the eulittoral subzone and 631 to 641 mg/kg in the infralittoral subzone. Both were much higher than that in the profundal zone (410 mg/kg). Calcium‐bound P (Ca‐P) was significantly correlated to exchangeable P (Ex‐P), and they both had the highest contents in the infralittoral subzone and the lowest in the profundal zone. The aluminum‐ and iron‐bound P (Al‐P, Fe‐P) contents decreased from land to water along the ecotone section. Lower Fe/P ratios and higher Al‐P/Fe‐P ratios appeared in the infralittoral subzone, as compared with the profundal zone. This suggested that the accumulated algae could lead to a great deposit of P in the littoral zones. However, the active sedimentary P form transformation in the littoral zones would also result in a partial release of the accumulated P to the overlying water. 相似文献
6.
华北汛期降水分离时间尺度降尺度预测模型的改进 总被引：2，自引：1，他引：1
本文采用偏相关预报因子挑选法和条件降尺度法,对已有的华北汛期(7~8月)降水时间尺度分离(TSD)降尺度模型进行了改进.利用偏相关法,找到一个新的影响华北汛期降水年际分量的前期预报因子,即6月北大西洋—欧亚遥相关(AEAT).该因子将扰动信号储存于北大西洋三极子结构,并在7~8月释放出来影响下游贝加尔湖低压系统的发展,从而影响华北汛期降水.利用6月Ni?o3指数和AEAT指数,本文建立了条件TSD统计降尺度模型,即按照预报因子的强度进行逐年分类,对于每个分类设计相应的预报模型,从而避免信息较弱因子的干扰.条件TSD降尺度方法显著改善了华北汛期降水的预测技巧,在独立检验阶段,预报降水与观测降水的相关系数由原模型的0.61提高到0.77,符号一致率从70%提高到87%. 相似文献
7.
单自由度陀螺罗盘寻北原理的研究 总被引：3，自引：0，他引：3
本文分析了单自由度陀螺罗盘在陀螺力矩、空气阻尼、摩擦力矩和悬挂带扭矩作用下的运动规律及其寻北原理，指出由于单自由度陀螺罗盘的摆动周期比二自由度陀螺罗盘的摆动周期显著缩短，定向速度可成倍提高，定向精度也有望提高，这将是陆地工程测量中子午线方位测量技术的一个重大进步 相似文献
8.
采用植硅体分析方法,对湖北荆门屈家岭遗址南部2015~2017年度主发掘区TN14W35探方内油子岭至石家河文化时期(5800~4200 a B.P.)的地层土样进行了系统取样分析,并重点对水稻扇型植硅体形态特征进行了研究.结果显示,遗址各文化时期土样中均含有丰富的水稻(Oryza sativa)特征型植硅体,表明稻作农业在屈家岭遗址各阶段先民植物资源的开发利用中始终占据着主导地位.同时,实验还在油子岭和屈家岭文化地层发现粟(Setaria italica)、黍(Panicum miliaceum)植硅体,但从发现数量看,粟类作物在屈家岭遗址先民农作物利用结构中只占据极小的比重.论文通过对水稻扇型植硅体形态参数测量和鱼鳞状纹饰统计发现,屈家岭遗址的水稻遗存主要属于粳稻类型,且驯化程度在油子岭文化早期时期就已经达到现代栽培稻水平.本文研究揭示了屈家岭遗址先民的农业结构、水稻类型及驯化水平,为了解江汉平原汉水东部地区新石器时代晚期人类生业形式与水稻驯化水平等提供了重要科学依据. 相似文献
9.
A comparative study of nutrient transfer via surface runoff from two small agricultural catchments in north China 总被引：1，自引：0，他引：1
A field study was conducted to determine the effect of landscape spatial pattern and micro-topography on nutrient transfer
via runoff from two catchments into Yuqiao Reservoir in north China. The surface runoff discharge was measured during rainfall
events and water samples were analyzed in 2004 and 2005. The mean annual total nitrogen (TN) and total phosphorus (TP) exports
per unit area from Caogezhuang catchment (C catchment) were 1.048 and 0.561 kg ha−1 year−1, respectively, while the TN and TP exports from Taohuasi catchment (T catchment) were 0.158 and 0.027 kg ha−1 year−1. In both catchments, village and vineyard shared the highest nutrient export ability due to the accumulated animal waste
and heavy application of fertilizer and manure. In T catchment, the distance of village and vineyard was about 1,500 m away
from the receiving water and in between were woodland and cropland. In the hydrological pathway, there were sink landscape
structures of small stone dams, roadside swale, vegetated filter strip and dry ponds, which could detain water and nutrients.
In C catchment, the distance between the village and the receiving water was about 200 m, and the hydrological pathway was
compacted roads and ditches with no sink structures. It is suggested that the distance between the pollution source area and
the receiving water and the micro-topographical features were the main factors to control the great difference in nutrient
export rates. 相似文献
10.
The flux of land-based source pollutants from tumen river system entering the sea of Japan 总被引：1，自引：0，他引：1
Ｉ．ＩＮＴＲＯＤＵＣＴＩＯＮ“Ａｇｅｎｄａ２１”ｒｅｃｏｇｎｉｚｅｓｔｈｅｉｍｐｏｒｔａｎｃｅｏｆｌａｎｄｂａｓｅｄｓｏｕｒｃｅｐｏｌｕｔａｎｔｓｔｏｍａｒｉｎｅｐｏｌｕｔｉｏｎ．Ｃｏａｓｔａｌｗａｔｅｒｉｓｏｆｇｒｅａｔｓｉｇｎｉｆｉｃａｎｃｅ... 相似文献